DogSource: Aucoin 2000
Gram-positive: 10 mg/kg · every 12 h · until ≥2 days after signs resolve
Antibiotic Therapy
Amoxicillin
Aminopenicillin (no beta-lactamase inhibitor) · bactericidal (cell-wall synthesis inhibitor)
Species: Dogs & Cats13 dose protocols8 dosage forms
This page is a calculation and educational reference for veterinarians and veterinary students. It does not replace examination, culture and susceptibility testing, clinical judgment, or the attending veterinarian's final decision.
Drug overview
Aminopenicillin (no beta-lactamase inhibitor) · bactericidal (cell-wall synthesis inhibitor)
Brand names: Amoxil®, Amoxi-Tabs®
General dose: 11–22 mg/kg PO · every 12 hSource: Plumb's/BSAVA (general)
Spectrum of activity
A broad-spectrum, bactericidal aminopenicillin with the same spectrum as ampicillin, but with much better oral absorption (serum levels 1.5–3× those of ampicillin) — so it is the preferred oral aminopenicillin. It is active against streptococci, enterococci, Listeria, many anaerobes (Clostridium, Fusobacterium), some aerobic Gram-negatives (susceptible E. coli, Proteus mirabilis, Pasteurella, Haemophilus) and spirochetes (Leptospira, Borrelia). But because it has no beta-lactamase inhibitor, it is inactive against beta-lactamase-producing bacteria — such as most Staphylococcus and Bacteroides fragilis (unlike co-amoxiclav). It also has no effect on Pseudomonas, Enterobacter, Citrobacter, Serratia, indole-positive Proteus, or cell-wall-free/intracellular bacteria (Mycoplasma, Rickettsia).
Veterinary uses and doses
By organism class
DogSource: Aucoin 2000
Gram-negative: 20 mg/kg · PO every 8 h or parenteral every 12 h
CatSource: Aucoin 2000
Cat, Gram-positive: 10 mg/kg · every 12 h · until ≥2 days after signs resolve
CatSource: Aucoin 2000
Cat, Gram-negative: 20 mg/kg · PO every 8 h or parenteral every 12 h
Urinary tract (sporadic cystitis)
DogSource: ISCAID 2019
Sporadic cystitis: 11–15 mg/kg PO · every 8 h · 3–5 days
Clinical note: Per ISCAID (2019), amoxicillin is first-line for sporadic cystitis; give a short 3–5 day course. Post-treatment culture is not needed.
CatSource: ISCAID 2019
Cat — sporadic cystitis: 11–15 mg/kg PO · every 8 h · 3–5 days
Sepsis / bacteremia
DogSource: Greene 2006
22–30 mg/kg parenteral · every 8 h · 7 days
CatSource: Greene 2006
Cat: 10–20 mg/kg · every 12 h
Orthopedic
DogSource: Greene 2006
22–30 mg/kg · every 6–8 h · 7–10 days
Lyme disease
DogSource: ACVIM (Lyme)
20–22 mg/kg PO · every 12 h · 30 days
Clinical note: Doxycycline is first-line for Lyme disease; amoxicillin is an acceptable alternative. The recommended course is about 30 days.
GI (Clostridium / Helicobacter)
CatSource: Lappin 2000
Cat C. perfringens / bacterial overgrowth: 22 mg/kg PO · once daily · 5 days
CatSource: Leib 2004
Cat C. perfringens enterotoxicosis: 11–22 mg/kg PO · 2–3 times daily · 7 days
CatSource: Simpson 2003
Cat Helicobacter (triple therapy): 20 mg/kg PO · every 12 h · 14 days
Combination therapy: with metronidazole 10–15 mg/kg and clarithromycin 7.5 mg/kg PO every 12 h
Dosage forms
- Suspension 250 mg/5 mL
- Suspension 125 mg/5 mL
- Suspension 200 mg/5 mL
- Suspension 400 mg/5 mL
- Capsule 250 mg
- Capsule 500 mg
- Tablet 875 mg
- Injectable vial 500 mg
Safety and clinical notes
- Amoxicillin has no beta-lactamase inhibitor, so it is inactive against beta-lactamase-producing bacteria (most staphylococci, Bacteroides fragilis) — use co-amoxiclav in those cases.
- It has good oral absorption (better than ampicillin); it can be given with or without food, but giving it with food helps if there is GI upset.
- Contraindicated in penicillin allergy; cross-reactivity with cephalosporins and carbapenems is possible.
- Never give to rabbits, guinea pigs, chinchillas or hamsters — risk of fatal enteritis and clostridial enterotoxemia (it is safe in dogs and cats).
- In septicemia or shock, oral absorption is reduced; use a parenteral route (preferably IV).
- The most common adverse effects are GI (anorexia, vomiting, diarrhea); it may alter gut flora and cause antibiotic-associated diarrhea.
- Store the reconstituted suspension refrigerated (preferably) and discard after 14 days.
- Considered relatively safe in pregnancy (class A in dogs and cats).
Cited sources
- Plumb's/BSAVA (general)
- Aucoin 2000
- ISCAID 2019
- Greene 2006
- ACVIM (Lyme)
- Lappin 2000
- Leib 2004
- Simpson 2003
Calculate a weight-based dose
Drug-data last updated: